Manufacturing method of joint panel

ABSTRACT

A manufacturing method of a joint panel includes: joining an outer panel to an inner panel by applying an adhesive to an outer edge of the outer panel; performing electrodeposition coating on a surface of the outer panel of the joint panel in which the outer panel is joined to the inner panel; and burning, onto the outer panel, a coating film formed on the surface of the outer panel by the electrodeposition coating. The adhesive used herein is a room temperature curing adhesive that does not flow at the time of the burning.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2014-075740 filed on Apr. 1, 2014 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of a joint panel in which an outer panel made of a metallic material is joined to an inner panel made of a material having a linear expansion coefficient different from a linear expansion coefficient of the metallic material.

2. Description of Related Art

In recent years, a panel such as a hood for an automobile has been manufactured as a joint panel in which an outer panel made of a metallic material is joined to an inner panel made of a material different from the metallic material. Aluminum alloy or a steel sheet such as high tensile strength steel is used as the metallic material of the outer panel, and a metallic material different from the outer panel, or a fiber reinforced plastic is used as the material of the inner panel.

The outer panel and the inner panel are made of different materials, so their linear expansion coefficients are different from each other. Because of the linear expansion coefficients, peeling of adhesion may occur due to shear stress (thermal stress) caused on adhesive surfaces. In view of this, Japanese Patent Application Publication No. 2007-118852 (JP 2007-118852 A) proposes such a manufacturing method of a joint panel that an outer panel is fixed to an inner panel by adhesion, and a bracket is fixed, by adhesion, to both the inner panel and the outer panel so as to cover at least part of an outer-panel outer-edge side of the inner panel from an outer edge of the outer panel.

Even if the peeling of adhesion is caused by shear stress (thermal stress) caused on the adhesive surfaces due to a difference between the linear expansion coefficients of the outer panel and the inner panel, it is possible to prevent the outer panel from falling off the inner panel by the bracket.

However, generally, the adhesive that bonds the outer panel to the inner panel is applied at the time when the outer panel and the inner panel are assembled, and after that, the adhesive is cured at the time when a coating film deposited by electrodeposition coating is burned onto the outer panel. Accordingly, when the coating film is burned, the outer panel is stretched in a range of elastic deformation due to heat of the burning, and in such a stretched state, the outer edge of the outer panel is restricted by the inner panel through the adhesive thus cured.

Consequently, the outer edge of the outer panel to be deformed to contract (restore) by cooling (standing to cool) after the coating film is burned is restricted by the inner panel through the cured adhesive, so that the deformation of the outer panel at the time of the burning is maintained. This may impair an appearance of the outer panel.

SUMMARY OF THE INVENTION

The present invention provides a manufacturing method of a joint panel, which manufacturing method can restrain deformation of an outer panel at a room temperature even in a case where coating/burning is performed on a surface of the outer panel in a state where outer edges of the outer panel and an inner panel are bonded via an adhesive.

A manufacturing method of a joint panel, according to one aspect of the present invention includes: joining an outer panel made of a metallic material to an inner panel made of a material having a linear expansion coefficient different from a linear expansion coefficient of the metallic material by applying an adhesive to either one of an outer edge of the outer panel and an outer edge of the inner panel and curing the adhesive; performing electrodeposition coating on a surface of the outer panel of the joint panel in which the outer panel is joined to the inner panel; and burning, onto the outer panel, a coating film formed on the surface of the outer panel by the electrodeposition coating, wherein the adhesive is a room temperature curing adhesive that does not flow at the time of the burning.

According to one aspect of the present invention, the room temperature curing adhesive is used when the outer panel is joined to the inner panel in the joining, so that the outer panel is joined to the inner panel by curing the adhesive without causing heat to act on the outer panel and the inner panel, thereby forming the joint panel.

The joint panel thus obtained is subjected to electrodeposition coating in the coating, and further, when the coating film is burned onto the outer panel in the burning, thermal stress temporarily acts on the outer panel due to a thermal expansion difference between the outer panel and the inner panel.

However, in the burning, the adhesive does not flow, so that the adhesive is maintained in a cured state. Accordingly, even if the outer panel is cooled off to a room temperature after the burning and the outer panel contracts, the thermal stress acting on the outer panel is removed. Hereby, the outer panel returns to its original shape, so that appearance of its coating surface is not impaired.

As such, in the joint panel after the burning, shear stress caused due to thermal stress hardly acts on adhesive surfaces of the outer panel and the inner panel at a room temperature, so that it is possible to secure reliability of the outer panel and the inner panel with the adhesive.

Particularly, in a case where the adhesive is provided to seal inner sides of the outer panel and the inner panel, its sealing characteristic can be secured. This makes it possible to restrain corrosion of the outer panel made of the metallic material.

Note that the “room temperature curing adhesive” is an adhesive that is cured only by natural drying without heating, so as to adhere two members. A two-component room temperature curing adhesive is generally known as the room temperature curing adhesive.

The metallic material of the outer panel may be aluminum alloy, and the material of the inner panel may be a fiber reinforced plastic. A linear expansion coefficient of the aluminum alloy is extremely larger than a linear expansion coefficient of the fiber reinforced plastic. Because of this, in a case where the aluminum alloy is used for the outer panel and the fiber reinforced plastic is used for the inner panel, a thermal expansion difference therebetween in the burning is larger than combinations of other materials. However, the adhesive is maintained in a cured state as described above, so it is possible to restrain deformation of the outer panel after the burning. Hereby, it is possible to sufficiently achieve a design property that the outer panel using aluminum alloy originally has, the design property is a design property based on coating glossy.

At the time of the joining, a hemming process may be performed such that the adhesive is applied to the outer edge of the outer panel, and the outer edge of the outer panel is folded toward the outer edge of the inner panel.

The adhesive is placed between the outer edge of the outer panel and the outer edge of the inner panel in the hemming process. Hereby, it is possible to prevent overflow of the adhesive. Further, even if the adhesive is peeled off at the time of the burning, the inner panel does not fall off the outer panel, because the outer edge of the inner panel is accommodated in a folded part (the outer edge) of the outer panel.

The adhesive may be a two-component epoxy adhesive. Hereby, it is possible to reduce surface deflection, which is a displacement amount of the joint panel after the burning.

According to one aspect of the present invention, it is possible to restrain deformation of an outer panel at a room temperature even in a case where coating/burning is performed on a surface of the outer panel in a state where outer edges of the outer panel and an inner panel are bonded via an adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a view illustrating each step to manufacture a joint panel according to an embodiment of the present invention;

FIG. 2 is a schematic perspective view illustrating an outer panel and an inner panel;

FIG. 3 is a schematic perspective view illustrating the joint panel in which the outer panel is joined to the inner panel;

FIG. 4 is a schematic sectional view illustrating a hemming structure of outer edges of the outer panel and the inner panel; and

FIG. 5 is a schematic perspective view to describe electrodeposition coating performed on a surface of the outer panel of the joint panel in which the outer panel is joined to the inner panel.

DETAILED DESCRIPTION OF EMBODIMENTS

The following describes an embodiment of the present invention with reference to the drawings. FIG. 1 is a view illustrating each step to manufacture a joint panel according to an embodiment of the present invention, and FIG. 2 is a schematic perspective view illustrating an outer panel and an inner panel. FIG. 3 is a schematic perspective view of the joint panel in which the outer panel is joined to the inner panel, and FIG. 4 is a schematic sectional view illustrating a hemming structure of outer edges of the outer panel and the inner panel. FIG. 5 is a schematic perspective view to describe electrodeposition coating performed on a surface of the outer panel of the joint panel.

First, an outer panel (an outer hood) 20 and an inner panel (an inner hood) 30 are prepared. The outer panel 20 is a panel made of aluminum alloy, which is a metallic material, and is a panel that is press molded in a shape illustrated in FIG. 2. Electrodeposition coating is performed on a surface of the outer panel 20 after the outer panel 20 is joined to the inner panel 30. In the present embodiment, as the metallic material of the outer panel 20, aluminum alloy is used from the viewpoint of lightweighting of the panel, but a steel sheet may be used, for example.

The inner panel 30 is made of a material having a linear expansion coefficient different from a linear expansion coefficient of the metallic material. Examples of the material include a metallic material different from the outer panel 20, a resin material, a fiber reinforced plastic, and the like. The fiber reinforced plastic, which is a material having a light weight and a high strength, is preferable among them.

The fiber reinforced plastic indicates a resin reinforced by a reinforcing fiber. The reinforcing fiber may be, for example, a fiber such as glass fiber, carbon fiber, aramid fiber, alumina fiber, boron fiber, steel fiber, PBO fiber, or high-strength polyethylene fiber.

The resin may be a thermo setting resin or a thermo plastic resin, and examples thereof include epoxy resin, phenolic resin, melamine resin, urea resin, silicone resin, maleimide resin, vinylester resin, unsaturated polyester resin, unsaturated polyethylene resin, polyurethane resin, cyanate resins, and polyimide resins.

In the present embodiment, the resin having such a reinforcing fiber is molded into a shape illustrated in FIG. 2. From the viewpoint of low cost, the inner panel 30 is made of a sheet molding compound (C-SMC) in which carbon of a thermo setting resin is a reinforcing fiber.

First, in S11 of FIG. 1, an adhesive is applied to an outer edge 21 of the outer panel 20 thus prepared, and the inner panel 30 is superimposed on the outer panel 20, as illustrated in FIG. 2. The adhesive used herein is a room temperature curing adhesive that does not flow in the after-mentioned step (a burning step) of burning a coating film.

Such an adhesive can be a two-component epoxy adhesive, and is preferably a two-component epoxy resin which includes a bisphenol-A epoxy resin, a bisphenol-F epoxy resin, a novolak epoxy resin, or the like as a base compound and which also includes an amine, polyamine, or mercaptan curing agent. The two-component epoxy resin may be a solventless resin, an organic solvent resin, or a water-based resin.

Then, in S12 of FIG. 1, a hemming process is performed with respect to the outer edge 21 of the outer panel 20 and an outer edge 31 of the inner panel 30, as illustrated in FIG. 3. More specifically, the outer edge 21 of the outer panel 20 is folded toward the outer edge 31 of the inner panel 30. Hereby, as illustrated in FIG. 4, the outer edge 21 of the outer panel 20 is placed so as to surround the outer edge 31 of the inner panel 30, and an adhesive 40 is placed between the outer edge 21 of the outer panel 20 and the outer edge 31 of the inner panel 30.

Then, in S13 of FIG. 1, the adhesive 40 is dried. In the present embodiment, the room temperature curing adhesive is used as the adhesive 40, so it is possible to join the outer panel 20 and the inner panel 30 by curing the adhesive without heating the outer panel 20 and the inner panel 30 (a joining step). Hereby, a joint panel 1 can be obtained.

Then, in S14 of FIG. 1, electrodeposition coating is performed on a surface 22 of the outer panel 20 of the joint panel 1 in which the outer panel 20 is joined to the inner panel 30. Hereby, a coating film 50 is formed on the surface of the outer panel 20.

In an electrodeposition coating step, the resin coating film 50 formed on the surface of the outer panel 20 is not cured. In view of this, in S15 of FIG. 1, the coating film 50 formed on the surface 22 of the outer panel 20 by electrodeposition coating is burned onto the outer panel 20 (the burning step). More specifically, the joint panel 1 is heated at a given temperature for a given time, so as to cure the coating film 50. Hereby, the coating film 50 is adhered to the surface of the outer panel 20. In the present embodiment, the adhesive that does not flow in the burning step is used as the adhesive 40, so the adhesive 40 can be maintained in a cured state at the time of the burning step.

As such, in the present embodiment, when the outer panel 20 is joined to the inner panel 30 in the joining step, the room temperature curing adhesive 40 is used. Accordingly, the joint panel (hood) 1 can be formed such that the outer panel 20 is joined to the inner panel 30 by curing the adhesive 40 without causing heat to act on the outer panel 20 and the inner panel 30.

The joint panel 1 thus obtained is subjected to electrodeposition coating in the coating step, and further, when the coating film 50 is burned onto the surface 22 of the outer panel 20 in the burning step, thermal stress temporarily acts on the outer panel 20 due to a thermal expansion difference between the outer panel 20 and the inner panel 30.

However, in the burning step, the adhesive 40 does not flow, so that the adhesive 40 is retained at a position where the adhesive 40 is applied and the adhesive 40 is maintained in a state where the adhesive 40 is adhered to an adherend. Accordingly, even if the outer panel 20 is cooled off to a room temperature after the burning step and the outer panel 20 contracts, the thermal stress acting on the outer panel 20 is removed. Hereby, the outer panel 20 returns to its original shape, so that appearance of its coating surface is not impaired.

Further, after the burning step, shear stress due to the thermal stress hardly acts on the adhesive 40 that adheres the outer panel 20 to the inner panel 30, at a room temperature. This makes it possible to secure reliability of adhesion between the outer panel 20 and the inner panel 30 with the adhesive 40.

Further, in the present embodiment, aluminum alloy is used for the outer panel 20, and a fiber reinforced plastic (particularly, a carbon fiber reinforced plastic) is used for the inner panel 30. In this case, in the burning step, a thermal expansion difference therebetween is larger than combinations of other materials. However, the adhesive is maintained in a cured state at the time of joining as described above, thereby making it possible to restrain deformation of the outer panel 20 after the burning step. Hereby, it is possible to sufficiently achieve a design property that the outer panel 20 using aluminum alloy originally has, the design property is a design property based on coating glossy.

Further, the hemming process is performed on the outer panel 20. Accordingly, even if the adhesive is peeled due to shear force in the burning step, the inner panel does not fall off the outer panel, because the outer edge of the inner panel 30 is accommodated in a folded part (the outer edge) of the outer panel.

The following describes examples of the present invention.

Example 1

An outer panel (outer hood) made of aluminum alloy (JIS: 6000 series aluminum alloy) having a shape illustrated in FIG. 2, an inner panel (inner hood) made of a carbon fiber reinforced plastic (C-SMC), and an adhesive that is a two-component epoxy adhesive (a product made by LORD Far East Incorporated: Fusor320/310BBlack, containing a base compound and a curing agent by 1:1) are prepared.

Then, the two-component epoxy adhesive is applied to an outer edge of the outer panel, and a hemming process is performed so as to fold the outer edge of the outer panel toward an outer edge of the inner panel, as illustrated in FIG. 4. After that, the two-component epoxy adhesive is cured under conditions of 30° C. (room temperature) and 70 minutes. Then, electrodeposition coating is performed on a surface of the outer panel, and a coating film formed on the surface of the outer panel by electrodeposition coating is burned under conditions of a heating temperature of 180° C. and a heating time of 20 minutes.

Images of an entire surface of a joint panel before and after the burning are taken, and on the basis of the joint panel before the burning, a displacement amount of the outer panel of the joint panel after the burning is measured. A result thereof is shown in Table 1. (A) to (F) shown in Table 1 indicate displacement amounts at respective measurement points shown in FIG. 3.

TABLE 1 Displacement amount at each measurement point (mm) (A) (B) (C) (D) (E) (F) Example 1 −2.5 7.5 −2.5 0.0 −2.5 −7.5 Example 2 −3.0 6.0 −2.5 0.0 −3.0 −6.0 Example 3 −3.0 7.5 −3.0 1.0 −3.0 −7.5 Comparative −2.5 2.5 −2.5 15.0 −5.0 −5.0 Example 1

Example 2

A joint panel is manufactured in the same manner as Example 1. A point different from Example 1 is as follows: an adhesive that is a two-component epoxy adhesive (a product made by LORD Far East Incorporated: Fusor320/322, containing a base compound and a curing agent by 1:1) is used as an adhesive. Then, similarly to Example 1, images of an entire surface of the joint panel before and after the burning are taken, and on the basis of the joint panel before the burning, a displacement amount of an outer panel of the joint panel after the burning is measured. A result thereof is shown in Table 1.

Example 3

A joint panel is manufactured in the same manner as Example 1. A point different from Example 1 is as follows: an adhesive that is a two-component epoxy adhesive (a product made by LORD Far East Incorporated: Fusor390/391, containing a base compound and a curing agent by 1:1) is used as an adhesive. Similarly to Example 1, images of an entire surface of the joint panel before and after the burning are taken, and on the basis of the joint panel before the burning, a displacement amount of an outer panel of the joint panel after the burning is measured. A result thereof is shown in Table 1.

Comparative Example

A joint panel is manufactured in the same manner as Example 1. A point different from Example 1 is that a one-component epoxy adhesive is used as an adhesive, and a coating film formed on a surface of an outer panel by electrodeposition coating is burned and the adhesive is cured under conditions of a heating temperature of 180° C. and a heating time of 40 minutes. Similarly to Example 1, images of an entire surface of the joint panel before and after the burning are taken, and on the basis of the joint panel before the burning, a displacement amount of the outer panel of the joint panel after the burning is measured. A result thereof is shown in Table 1.

<Result 1 and Consideration 1>

In a case of the joint panels of Examples 1 to 3, the adhesive is cured in advance by drying in the joining step, so that the outer panel elastically deformed by expansion in the burning step is restored to its original state after cooling. Accordingly, the displacement amount as a surface deflection at the point (D) is smaller than that of the comparative example. In the meantime, in a case of the joint panel of the comparative example, the adhesive is cured at a point when the outer panel is elastically deformed by expansion in the burning step. As a result, the deformation is maintained, so that the displacement amount as a surface deflection at the point (D) is larger than those of Examples 1 to 3.

Reference Examples 1 to 3

An aluminum alloy plate (JIS: 6000 series aluminum alloy) with 25 mm×70 mm×0.9 mm, corresponding to an outer panel, and a carbon fiber reinforced plastic plate (C-SMC) with 25 mm×70 mm×2.0 mm, corresponding to an inner panel, are prepared. The adhesives according to Examples 1 to 3 are prepared as adhesives for Reference Examples 1 to 3.

The aluminum alloy plate thus prepared is degreased by isopropyl alcohol (IPA), and the carbon fiber reinforced plastic plate is degreased by dry wipe. Then, these plates are dipped in rust preventive oil (a product made by Sugimura Chemical Industrial Co., Ltd., PRETON 303PX2), and left for 24 hours or more.

Each of the adhesives is applied to the aluminum alloy plate and the carbon fiber reinforced plastic plate after the dipping, so that an adhesive thickness is 0.25 mm and an adhesion area is 25 mm×12.5 mm, and the each of the adhesives is cured under conditions of 30° C. (room temperature) and 70 minutes. Then, a heating process corresponding to the burning step is performed at a heating temperature of 180° C. for a heating time of 20 minutes.

In order to perform three-level measurement, in each test described below, on the joint panels in each of which the aluminum alloy plate is joined to the carbon fiber reinforced plastic plate through each of the adhesives of Reference Examples 1 to 3, test pieces are prepared.

More specifically, a shearing test (JISK6850) is performed under conditions of an elastic stress rate of 5 mm/min, a chuck-to-chuck distance of 90 mm, and a test temperature of 25° C., so as to measure a shear strength between the aluminum alloy plate and the carbon fiber reinforced plastic plate. A result thereof is shown in Table 2. Table 2 shows an average value of the shear strength measured three times for each of Reference Examples 1 to 3.

Further, a cross peel test is performed at an elastic stress rate of 5 mm/min and at a test temperature of 25° C., so as to measure a breaking strength between the aluminum alloy plate and the carbon fiber reinforced plastic plate. A result thereof is shown in Table 2. Table 2 shows an average value of the breaking strength measured three times for each of Reference Examples 1 to 3.

Furthermore, a breaking mode of the aluminum alloy plate in each of the tests is further observed. A result thereof is shown in Table 2. Note that, in Table 2, AF indicates an interfacial failure, CF indicates an adhesion cohesive failure, TCF indicates a thin layer adhesive cohesive failure, and respective values shown subsequently thereto each indicate an area ratio.

TABLE 2 Shearing Test Cross Peel Test Strength Breaking Strength Breaking (MPa) Mode (N/25 mm) Mode Reference 13.6 AF  0% 476 AF  0% Example 1 CF 95% CF 100% TCF  5% TCF  0% Reference 11.1 AF  0% 446 AF  0% Example 2 CF 98% CF 100% TCF  2% TCF  5% Reference 7.1 AF 50% 352 AF  95% Example 3 CF 50% CF  5% TCF  5% TCF  0%

<Result 2 and Consideration 2>

From the result of Reference Examples 1 to 3, in a case where the adhesives of Reference Examples 1, 2 are used, a breaking ratio of the adhesion cohesive failure (CF) is large, so that it is considered that the aluminum alloy plate and the carbon fiber reinforced plastic plate are in a particularly good adhesion state.

The embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and various design modifications can be made without departing from the spirit of the present invention described in Claims. 

What is claimed is:
 1. A manufacturing method of a joint panel, comprising: joining an outer panel made of a metallic material to an inner panel made of a material having a linear expansion coefficient different from a linear expansion coefficient of the metallic material by applying an adhesive to an outer edge of an outer edge of the outer panel and an outer edge of the inner panel and curing the adhesive; performing electrodeposition coating on a surface of the outer panel of the joint panel in which the outer panel is joined to the inner panel; and burning, onto the outer panel, a coating film formed on the surface of the outer panel by the electrodeposition coating, wherein the adhesive is a room temperature curing adhesive that does not flow at the time of the burning.
 2. The manufacturing method of the joint panel, according to claim 1, wherein: the metallic material of the outer panel is aluminum alloy; and the material of the inner panel is a fiber reinforced plastic.
 3. The manufacturing method of the joint panel, according to claim 1, wherein: at the time of the joining, a hemming process is performed such that the adhesive is applied to the outer edge of the outer panel, and the outer edge of the outer panel is folded toward the outer edge of the inner panel.
 4. The manufacturing method of the joint panel, according to claim 1, wherein the adhesive is a two-component epoxy adhesive. 